I hope this is the right section, I'm not sure what's causing it but figured here is a good start to trouble shooting. It's a completely stock system.

I will be driving down the road all fine then my sound will suddenly decrease, not cut out, just sounds like I turned it down a few clicks. Then eventually it will randomly come back up to normal playing level. It seems to be 100% random, I can't recreate the effect no matter what I try. It's also not constant, may happen once every 5 mins or only once in an hour. Any ideas or help is greatly appreciated!

 

Have you tried messing with the speed volume in the menu? I know the F250 has it but I'm not sure about the F150.

 

A little insight. My 04 F150 was "muting" the volume everytime I stepped on the brake. I didn't wait (my bad) to see if it would come up on it's own, so I just turned volume back up manually. Step on brake again, muted again. Like yours, not completely killing the sound, just turned it down, probably 50%.

I found that there is a wire going to the radio, thru the body control module and from the backup alarm, that muted the radio when backup alarms sounded off. I snipped that wire and problem stopped, with no other effects. That pesky backup alarm is loud (and irritating) enough to wake the dead and there is no need to mute the radio for it, even if radio is up loud. Plus I didn't want to spend the huge bucks on a new Body Control Module to make the problem stop, if I didn't absolutely have to. Yeah, I know, I'm a cheap skate.

Don't know if this is same as your problem, but it might be..

 

This. Does the volume vary with your speed?

- NCSU

 

no it seems to be completely irrelevant of vehicle speed, rpm, pedals, truck/battery voltage. My only guess is some component in the head unit is going out, kind of costly to replace it and find out that wasn't the problem though. Is there any cheaper stereo related electronic components I could replace as a starting point?